In recent years, semiconductor devices with light-detecting sensors (also referred to as photosensors, photosensor circuits, or photoelectric conversion circuits) have attracted attention. For example, display devices with photosensors used as touch sensors, are called touch panels, touch screens (also referred to as touch panels), or the like. The touch panel includes photosensors in a display area and thus the display area also functions as an input area. An example of touch panels is display devices with an image capture function (see Patent Document 1, for example). Examples of semiconductor circuits including a photosensor are CCD image sensors and CMOS image sensors. Semiconductor circuits such as CCD image sensors or CMOS image sensors are used, for example, in electronic appliances such as digital still cameras or cellular phones.
In a display device with photosensors, light emitted by the display device is reflected by an object and the photosensors in a pixel portion of the display device detect the reflected light; thus, the existence of the object over the pixel portion can be recognized. Further, in a display device with a photosensor, light emitted by an object or light reflected by an object is detected by the photosensor directly or after the light is gathered by an optical lens or the like.